1. Field of the Invention
The present invention relates to multifilament suture yarn and to a method for making same.
2. Background of the Art
Sutures intended for the repair of body tissues must meet certain requirements: they must be substantially non-toxic, capable of being readily sterilized, they must have good tensile strength and have acceptable knot-tying and knot-holding characteristics and if the sutures are of the absorbable or biodegradable variety, the absorption or biodegradation of the suture must be closely controlled.
Sutures have been constructed from a wide variety of materials including surgical gut, silk, cotton, a polyolefin such as polypropylene, polyamide, polyglycolic acid, polyesters such as polyethylene terephthalate and glycolide-lactide copolymer, etc. Although the optimum structure of a suture is that of a monofilament, since certain materials of construction would provide a stiff monofilament suture lacking acceptable knot-tying and knot-holding properties, sutures manufactured from such materials are preferably provided as braided structures. Thus, for example, sutures manufactured from silk, polyamide, polyester and bio-absorbable glycolide-lactide copolymer are usually provided as multifilament braids. Commercial examples of such sutures include DEXON (David & Geck, Inc.) and VICRYL (Ethicon, Inc.).
Typically, braided sutures comprise an arrangement of discrete units, or bundles, denominated "sheath yarns", each sheath yarn being made up of individual filaments with the sheath yarns interlacing in a regular criss-cross pattern.
Optionally a core component may be included. The core may be a cabled structure made up of plied yarns each of which has been given a twist in one direction, the plied yarns then being combined to form a core which is then given a twist in a second, opposite direction.
As spun or zero twist yarn consists of filaments which are essentially parallel to each other and which are held in contiguity by a treating fluid, i.e., spin finish, which includes lubricants and other agents to facilitate processing of the yarn. As spun yarn is subject to defects which impair handling and processing characteristics of the yarn and the finished suture. For example, filaments can snag and break during processing, thereby causing defects such as fluff balls, slubs, and ringers. The surface characteristics of the finished suture are very important and must research and development has been performed in the suture field to improve the surface characteristics, especially the surface smoothness, of multifilament sutures. Surface defects caused by broken filaments add to the roughness of the suture and increases the "drag" or "chatter" of the suture at it is drawn through body tissue. Trauma to tissue is increased as a rough suture is pulled through tissue. Such defects, therefore, militate against smooth, neat, accurately placed wound approximation so necessary to excellence in surgical practice.
One way of reducing the defects mentioned above is to twist the individual filaments. Twisting compacts and unifies the yarn thereby resulting in a more cohesive structure. However, twisting greatly increases the processing costs. Moreover, as the yarn is subjected to an extra step of mechanical handling, it is more subject to be damaged. The fewer operations the filaments are subjected to during processing the less chance there is of breakage.
Another consideration is the denier of the individual filaments. From the standpoint of surface characteristics lower denier filaments are preferable for reducing the surface roughness and the attendant drag and chatter as the suture is drawn through body tissue. However, smaller denier filaments break more easily than larger denier filaments in certain processing.
What is needed, then, is a method which allows the manufacture of suture yarn without the twisting operation and having as few or fewer defects per length of suture as compared with currently used methods.